JPH04225577A - Light emitting diode - Google Patents

Abstract

PURPOSE:To improve a light emitting efficiency by injecting a current only to a region effective to emit a light from its surface in a surface light emission type light emitting diode. CONSTITUTION:An n-type AlGaAs layer 7, a p-type AlGaAs layer 3, an n-type AlGaAs layer 4 are sequentially laminated on an n-type GaAs substrate 1, and with an SiN film 5 as a mask a diffused region 8a and a connecting region 8b are formed. A p-type electrode 6 is formed on the region 8b, and an n-type electrode 7 is formed on the lower part of the substrate 1. Since the lower part of the electrode 6 is formed in a reverse bias structure, injection of a current is prevented, the current is injected only to the region 8a, and a light can externally be emitted without reflecting on the electrode 6.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light emitting diode, particularly a surface emitting type light emitting diode.

0002

2. Description of the Related Art A light emitting diode array consisting of a plurality of PN junction light emitting diodes arranged on a substrate has the advantage that image information can be processed relatively easily by electrically controlling each light emitting diode. Therefore, improvements and various applications are being considered.

For example, in a printer as an information output device, there is a demand for higher speed and higher density, and in order to satisfy this demand, it has been considered to use a light emitting diode array as a light source.

Namely, as non-impact optical printers, there are known laser printers that use a laser as a light source and LED printers that use a light emitting diode array as a light source. Whereas mechanisms such as polygon mirrors and corresponding complicated optical systems are required, LED printers can be driven by electrically controlling each light-emitting diode in a light-emitting diode array consisting of multiple light-emitting diodes. Therefore, compared to laser printers, they can be smaller, faster, and more reliable.

FIG. 5 shows a cross-sectional view of a light emitting diode used in a conventional LED printer or the like. In the figure, the light emitting diode consists of an n-GaAsP layer 9 on an n-GaAs substrate 1.
VPE (Vapor Phase Epitax)
y) method, and then Zn is diffused using the SiN film 5 as a mask to form an island-shaped Zn diffusion region 8, and the interface between the n-GaAsP layer 9 and this Zn diffusion region 8 forms a PN junction. It forms a surface and becomes a light emitting region.

The structure is such that a p-electrode 6 and an n-electrode 7 are formed respectively, and light from the PN junction surface is emitted from the surface by applying a predetermined voltage between the two electrodes.

[0007]

[Problems to be Solved by the Invention] However, in such a surface-emitting type light emitting diode, the p-electrode 6
The lower part of the electrode has the highest current density and is where the most light is emitted, but the light emitted from this area is reflected by the p-electrode 6 and is not taken out to the outside, resulting in a significant drop in luminous efficiency. There was a problem with it.

The present invention was made in view of the above-mentioned conventional problems, and its purpose is to suppress light emission at the bottom of the electrode in a surface-emitting type light emitting diode, and to inject current only into the area where light emission to the outside is effective. In particular, it is an object of the present invention to provide a light emitting diode having extremely high luminous efficiency.

[0009]

[Means for Solving the Problems] In order to achieve the above object, a light emitting diode according to the present invention includes a P-type or N-type semiconductor layer formed on a substrate, a diffusion region formed in this semiconductor layer, and an electrode formed on the diffusion region, characterized in that the light emitting diode has a current blocking region below the electrode.

0010

[Function] The light emitting diode of the present invention has such a structure, and the current blocking region formed at the bottom of the electrode prevents light emission at the bottom of the electrode, and current is injected only into the diffusion region that is effective for light emission. By emitting light, reflection at the electrodes is reduced and luminous efficiency is improved.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the light emitting diode according to the present invention will be described below with reference to the drawings.

FIG. 1 shows a cross-sectional view of the light emitting diode of the first embodiment, in which n-Al is formed on an n-GaAs substrate 1.
GaAs layer 2, p-AlGaAs layer 3 and n-AlGa
As layers 4 are sequentially laminated by MBE method or the like. next,
Zn is diffused using the SiN film 5 as a mask to separate and form island-shaped diffusion regions 8a, and Zn is diffused again to connect both diffusion regions 8a with the Zn region. The depth of the diffusion region 8a is set to reach the p-AlGaAs layer 3, and the depth of the connection region 8b is set to reach the p-AlGaAs layer 3.
The layer thickness is set smaller than the layer thickness of layer 4. To perform Zn diffusion, it is sufficient to form a Zn0 film or the like containing a diffusion source Zn on the SiN film 5 by a sputtering method or the like, and leave it at a high temperature of 650° C. to 800° C. for several hours to thermally diffuse Zn. .

[0013] Then, the p+ contact layer is in the diffusion region 8a.
, a p-electrode 6 is formed on the connection region 8b, and an n-electrode 7 is further formed on the lower part of the n-GaAs substrate 1, thereby configuring the light emitting diode of this embodiment.

When a voltage is applied between the p-electrode 6 and the n-electrode 7, the lower part of the p-electrode 6 becomes p+, n, p, n, and n type in order from the substrate surface, resulting in a reverse bias structure. Therefore, no current is injected and light emission in this portion can be suppressed.

On the other hand, in the diffusion region 8a other than the lower part of the p- electrode 6, p+, p, n,
Since the current is injected into the entire diffusion region 8a through the p+ layer on the substrate surface, light is emitted at the PN junction formed at the interface between the n-AlGaAs layer 2 and the p-AlGaAs layer 3, and this light is It is taken out to the outside without being reflected by the p-electrode 6.

In this way, in the first embodiment, p-
By forming a current blocking region with a reverse bias structure at the bottom of the electrode 6, light emission from the bottom of the electrode is suppressed, and light is efficiently emitted from a diffusion region other than the bottom of the electrode, resulting in extremely high light emission efficiency. A light emitting diode can be obtained.

Note that in the first embodiment, n-AlGa
By appropriately selecting the composition ratios of Al, Ga, and As in the As layer 2, p-AlGaAs layer 3, and n-AlGaAs layer 4 (reducing the composition ratio of Al in the p-AlGaAs layer 3).
, the band gap of the n-AlGaAs layer 4 is set to p-AlG
The bandgap can be set smaller than that of aAs3, and at this time, the light emitted at the PN junction surface is
Since the light is not absorbed by the GaAs layer 4, the external light emission efficiency can be further increased.

FIG. 2 shows a cross-sectional view of a light emitting diode according to a second embodiment of the present invention. In the second embodiment, the PN junction surface where light emission occurs is not formed by crystal growth as shown in the first embodiment, but is formed by thermal diffusion. That is, the n-GaAs substrate 1
On top are an n-AlGaAs layer 2, a p-AlGaAs layer 3, and an n-AlGaAs layer 2.
-AlGaAs layers 4 are sequentially stacked, and Zn diffusion region 8a is formed using SiN film 5 as a mask until reaching n-AlGaAs layer 2. Thereafter, a connection region 8b is formed by diffusion in the same manner as in the first embodiment, and a p- electrode 6 and an n-electrode are formed on this connection region 8b via a p+ contact layer.
- An n- electrode 7 is formed under the GaAs substrate 1.

In the second embodiment, as in the first embodiment, a current blocking region having a p+, n, p, n, n type reverse bias structure is formed below the p- electrode 6. Therefore, no light is emitted from this region, and the diffusion region 8a and n-A
Light is emitted at the PN junction formed at the interface with the lGaAs layer 2, and is taken out to the outside without being reflected by the p-electrode 6.

In the second embodiment, as in the first embodiment, the band gap of the n-AlGaAs layer 4 can be set small to suppress light absorption and improve the luminous efficiency.

A third embodiment of the present invention is shown in FIGS. 3 and 4. In this third embodiment, an electrode is arranged around the outer periphery of the light emitting region, and a diffusion region formed in the light emitting region is provided with an electrode. Electric current is supplied from the electrodes.

That is, as shown in FIG.
n-AlGaAs layer 2 and p-AlGa on aAs substrate 1
An As layer 3 and an n-AlGaAs layer 4 are sequentially laminated, and the Si
Using the N film as a mask, place a Zn diffusion region 8 in the region where you want to obtain light emission.
form a. At this time, the diffusion region 8 is p-AlGaA
It is diffused until it reaches the S layer 3. Then, the SiN film is removed and the connection region 8b is formed by thermal diffusion, and then the p-electrode 6 is formed so as to surround the diffusion region 8a.

When a voltage is applied between the p-electrode 6 and the n-electrode 7, there is a current blocking region with a reverse bias structure under the p-electrode 6, as in the first and second embodiments. No light is emitted, and on the other hand, current is injected into the entire surface of the diffusion region 8a in a forward bias configuration, so that a continuous light emission pattern can be obtained.

Note that in the third embodiment, the p-electrode 6
Since the contact area between the LED and the substrate surface can be increased, it is also possible to reduce the series resistance of the light emitting diode.

[0025]

As explained above, according to the light emitting diode according to the present invention, it is possible to inject current only into the area effective for light emission from the surface, and extremely high light emitting efficiency can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a first embodiment of a light emitting diode according to the present invention.

FIG. 2 is a sectional view of a second embodiment of a light emitting diode according to the present invention.

FIG. 3 is a plan view of a third embodiment of a light emitting diode according to the present invention.

FIG. 4 is a sectional view of a third embodiment of a light emitting diode according to the present invention.

FIG. 5 is a cross-sectional view of a conventional light emitting diode.

[Explanation of symbols]

1 n-GaAs substrate 2 n-AlGaAs layer 3 p-AlGaAs layer 4 n-AlGaAs layer 5 SiN film 6 p-electrode 7 N-electrode 8a Diffusion area 8b Connection area

Claims (1)

[Claims] 1. A light emitting diode comprising a P-type or N-type semiconductor layer formed on a substrate, a diffusion region formed in this semiconductor layer, and an electrode formed on the diffusion region, wherein the electrode A light emitting diode characterized by having a current blocking region at the bottom.